(1) Field of the Invention
This invention is concerned with lockstitch sewing means, especially, but not exclusively, lockstitch sewing machines for use in the shoe industry where, for example, outsoles of thick, tough material, e.g. leather, are stitched to welts in the production of welted shoes.
(2) Prior Art
There is described in UK Patent Specification No. 410463 a lockstitch sewing machine comprising stitch forming instrumentalities, including a reciprocating hooked needle, on to the hook of which a loop of (needle) thread can be looped, when the needle has penetrated a workpiece and while it is projecting therethrough, and also a rotatable shuttle, by which the loop of thread is engaged, after retraction of the needle, and a lockstitch is formed using said loop and a further (bobbin) thread, thread measuring means for supplying a measured quantity of needle thread for each stitch formation, means, arranged "upstream" of the stitch forming instrumentalities, for clamping the thread after the measured quantity has been supplied as aforesaid, and means, arranged between the thread clamping means and the stitch forming instrumentalities, and including a thread take-up arrangement, by which said measured quantity of thread is controlled during stitch formation and by which also a formed lockstitch can be drawn into the body of the workpiece, such drawing of the formed stitch taking place while the thread remains clamped by the thread clamping means, but after the start of the formation of the next following stitch.
It will be appreciated that, at the end of a machine stitching cycle (i.e. at the end of a series of stitches), the workpiece can be removed from the operating locality only if the stitch forming instrumentalities are out of penetrating engagement therewith. However, bearing in mind that the setting of each stitch takes place only after the start of the formation of the next following stitch, the problem arises that the final stitch formed in a machine stitching cycle cannot be properly set. Instead, it is usually left to the operator to pull on the needle thread, thereby drawing the formed lockstitch into the body of the workpiece. In some machines, e.g. the machine described in the aforementioned patent specification, the stitch is almost set at the end of a stitch forming cycle, but in other machines the situation may arise where the stitch is not set until well after the start of the next stitch formation. In any event, relying on the operator to set the final stitch is generally unreliable since not only can the operator overlook to do so, but further the distance by which the formed stitch is drawn into the body of the work cannot be reliably controlled.
It is thus the object of the present invention to provide an improved lockstitch sewing machine in which the setting of the final stitch formed in a machine stitching cycle can be reliably and accurately controlled.